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Low-Temperature Sterilization: Characteristics, Benefits, Monitoring
William A. Rutala, PhD, MPHDirector, Hospital Epidemiology, Occupational Health
and Safety at UNC Health Care System; Professor of Medicine and Director, Statewide Program for
Infection Control and Epidemiology at University of North Carolina at Chapel Hill, USA
Disclosure-3M
Low-Temperature Sterilization
Provide overview of low-temperature sterilizationCharacteristicsBenefits Monitoring
www.disinfectionandsterilization.org
Disinfection and Sterilization in Healthcare FacilitiesWA Rutala, DJ Weber, and HICPAC, www.cdc.gov
Overview Last Centers for Disease Control and Prevention guideline
in 1985 158 pages (>82 pages preamble, 34 pages
recommendations, glossary of terms, tables/figures, >1000 references)
Evidence-based guideline Cleared by HICPAC February 2003; delayed by FDA Published in November 2008
Disinfection and Sterilization EH Spaulding believed that how an object will be disinfected
depended on the object’s intended use.CRITICAL - objects which enter normally sterile tissue or the
vascular system or through which blood flows should be sterile.
SEMICRITICAL - objects that touch mucous membranes or skin that is not intact require a disinfection process (high-level disinfection [HLD]) that kills all microorganisms but high numbers of bacterial spores.
NONCRITICAL -objects that touch only intact skin require low-level disinfection (or non-germicidal detergent).
Efficacy of Sterilization Influencing Factors
Cleaning of the objectOrganic and inorganic load presentType and level of microbial contaminationConcentration of and exposure time to disinfectant/sterilantNature of the objectTemperature and relative humidity
Processing “Critical” Patient Care ObjectsClassification: Critical objects enter normally sterile tissue or
vascular system, or through which blood flows.
Object: Sterility.Level germicidal action: Kill all microorganisms, including bacterial
spores.Examples: Surgical instruments and devices; cardiac
catheters; implants; etc.Method: Steam, gas, hydrogen peroxide gas plasma,
vaporized hydrogen peroxide, ozone or chemical sterilization.
Critical ObjectsSurgical instrumentsCardiac catheters Implants
SterilizationThe complete elimination or destruction of all forms of microbial life and is accomplished in healthcare facilities by either physical or chemical processes
Sterilization of Patient Equipment
Alternatives to ETO-CFCETO-CO2, ETO-HCFC, 100% ETO
Newer Low Temperature Sterilization TechnologyHydrogen Peroxide Gas PlasmaVaporized hydrogen peroxideOzone-not commonly used
Cleaning Mechanical cleaning machines-automated equipment may
increase productivity, improve cleaning effectiveness, and decrease worker exposure Utensil washer-sanitizer Ultrasonic cleaner Washer sterilizer Dishwasher Washer disinfector
Manual
STERILIZATIONFactors affecting the efficacy of sterilization Bioburden Cleaning Pathogen type Protein and salt Biofilm accumulation Lumen length and diameter Restricted flow
Lumens Sterilized by VariousLow-Temperature Sterilization Methods
Challenge: 12/88 100%ETO HCFC-ETO Sterrad10% Serum,0.65% Salt(7 organisms, N=63) 44% 39.7% 49.2% 35%No Serum or Salt,(3 organisms, N=27) ND 96.3% 96.3% NDAlfa et al. Infect Cont Hosp Epidemiol 1996;17:92-100. The three organisms included: E. faecalis, M.
chelonei, B. subtilis spores. The seven organisms included: E. faecalis, P. aeruginosa, E.coli, M. chelonei, B. subtilis spores, B. stearothermophilus spores, B. circulans spores
Low-Temperature Sterilization Technologies (LTST)Conclusions
All LTST technologies have limitations LTST (ETO, HP gas plasma) demonstrate a significant
number of failures in presence of serum or salt Salt and serum provide protection for spores and
bacteria Salt and serum combined with a narrow lumen provide
extraordinary protection with LTST
IS THERE A STANDARD TO DEFINE WHEN A DEVICE IS CLEAN?
There is currently no standard to define when a device is “clean”, cleanliness controlled by visual
Potential methods: level of detectable bacteria; protein (6µg/cm2); endotoxin; ATP; lipid
This is due in part to the fact that no universally accepted test soils to evaluate cleaning efficiency and no standard procedure for measuring cleaning efficiency
At a minimum, a cleaning process should: reduce the natural bioburden; remove organic/inorganic contaminants; provide devices that when sterilized have a SAL 10-6
Verifying Cleaning Processes AAMI recommends incorporating test methods that verify
the functionality of the automated washer Washer indicators have been in use in Europe and
Canada and some US hospitals Washer indicators are chemical indicators imprinted with a
dried test soil formula and a dye.
Cleaning Indicators for Washers Monitor the automated
washer and instrument cleaning chemistry functionaiity
Indicator includes proteins, lipids, and polysaccharides to mimic common challenging test soils
Low-Temperature Sterilization Provide overview of low-temperature sterilization
Characteristics Benefits-sterilize temperature and moisture-sensitive
medical and surgical devices in health care Review advantages/disadvantages of LTS technology
Monitoring
100% Ethylene Oxide4.8 ft3 chamber
Ethylene Oxide (ETO) Advantages
Very effective at killing microorganisms Penetrates medical packaging and many plastics Compatible with most medical materials Cycle easy to control and monitor
Disadvantages Some states (CA, NY, TX) require ETO emission reduction of 90-
99.9% (air pollution control device) CFC (inert gas that eliminates explosion hazard) banned after 1995 Potential hazard to patients and staff Lengthy cycle/aeration time
Ethylene Oxide Aeration• The ability to penetrate is an important characteristic of
ETO• It is this property that necessitates extended periods of aeration
• During aeration, heated air is flushed through chamber to remove ETO residuals from sterilized items
• Consult the medical device manufacturer for recommended aeration times• Composition of device
• Intended application
Aeration Time Guidelines*
Temperature Aeration Time
50°C 12 hours
60°C 8 hours
* Based on polyvinylchloride (PVC) tubing
Ref: ANSI/AAMI ST41:2008 Section 8.8.4
Ethylene Oxide Aeration
OSHA Occupational Exposure Standard for ETOExposure Limits
Employer required to monitoremployee exposure WHAT?
• Monitor for 8-hour TWA
• 15 minute sampling period
HOW?• Breathing zone air samples
WHO?• Representative employee on each shift for each job classification
If ETO exposure 0.5 ppm Action Level, 8-hr TWA-monitoring of those employees can be discontinued
3M™ Ethylene Oxide Monitor 3550
Hydrogen Peroxide Gas Plasma
Hydrogen Peroxide Gas Plasma Sterilization
Advantages Safe for the environment and health care worker; it leaves
no toxic residuals Fast - cycle time is 28-52 min and no aeration necessary Used for heat and moisture sensitive items since process
temperature 50oC Simple to operate, install, and monitor Compatible with most medical devices
Hydrogen Peroxide Gas Plasma Sterilization
Disadvantages Cellulose (paper), linens and liquids cannot be processed Sterilization chamber , about 3.5ft3 to 7.3ft3
Endoscopes or medical devices restrictions based on lumen internal diameter and length (see manufacturer’s recommendations); expanded claims with NX
Requires synthetic packaging (polypropylene) and special container tray
V-PRO™1, Vaporized Hydrogen Peroxide Advantages
Safe for the environment and health care worker; it leaves no toxic residuals
Fast - cycle time is 55 min and no aeration necessary Used for heat and moisture sensitive items (metal and nonmetal devices)
Disadvantages Sterilization chamber is small, about 4.8ft3
Medical devices restrictions based on lumen internal diameter and length-see manufacturer’s recommendations, e.g., SS lumen 1mm diameter, 125mm length
Not used for liquid, linens, powders, or any cellulose materials Requires synthetic packaging (polypropylene) Limited use and limited comparative microbicidal efficacy data
Ozone Advantages
Used for moisture and heat-sensitive items Ozone generated from oxygen and water (oxidizing) No aeration because no toxic by-products FDA cleared for metal and plastic surgical instruments, including
some instruments with lumens Disadvantages
Sterilization chamber small, 4ft3
Limited use (material compatibility/penetrability/organic material resistance?) and limited microbicidal efficacy data
ConclusionsSterilization
All sterilization processes effective in killing spores Cleaning removes salts and proteins and must precede
sterilization Failure to clean or ensure exposure of microorganisms
to sterilant (e.g. connectors) could affect effectiveness of sterilization process
RecommendationsMethods of Sterilization
Steam is preferred for critical items not damaged by heat Follow the operating parameters recommended by the
manufacturer (times, temperatures, gas conc) Use low temperature sterilization technologies for
reprocessing critical items damaged by heat Aerate surgical and medical items that have been
sterilized in the ETO sterilizer
Newer Trends in Sterilization of Patient Equipment
Alternatives to ETO-CFCETO-CO2, ETO-HCFC, 100% ETO
New Low Temperature Sterilization Technology
Hydrogen peroxide gas plasma-most common
Vaporized hydrogen peroxide-limited clinical useOzone and hydrogen peroxide-not FDA cleared
Nitrogen dioxide-not FDA cleared
Low-Temperature Sterilization Provide overview of low-temperature sterilization
Characteristics Benefits-sterilize temperature and moisture-sensitive
medical and surgical devices in health care Monitoring
Monitoring of Sterilizers Use physical, chemical and biological monitors to ensure the
effectiveness of the sterilization process Each load should be monitored with physical and chemical
indicators If the physical, chemical or biological indicators suggest
inadequate processing, the items should not be used Biological indicators should be used at least weekly (commonly
daily or each load) with spores intended specifically for the type of sterilizer
Objectives of Monitoring the Sterilization Process
Assures probability of absence of all living organisms on medical devices being processed
Detect failures as soon as possibleRemoves medical device involved in failures
before patient use
Sterilization MonitoringSterilization monitored routinely by combination of physical,
chemical, and biological parameters Physical - cycle time, temperature, pressure Chemical - heat or chemical sensitive inks that change
color when germicidal-related parameters present (Class 1-6)
Biological - Bacillus spores that directly measure sterilization
Biological Indicators • Select BIs that contain spores of
Bacillus atrophaeus
• Rationale: BIs are the onlysterilization process monitoringdevice that provide a direct measure of the lethality of the process
Biological Monitors ETO - B. atrophaeus New low temperature sterilization technologies
HP gas plasma (Sterrad) and HP vapor (V-Pro)- G. stearothermophilus
Ozone-G. stearothermophilus
Process Challenge Device (PCD)
“A PCD is a device used to assess the effective performance of a sterilization process by providing a challenge to the process that is equal or greater than the challenge posed by the most difficult item routinely processed.”
•PCD may be:
• User-assembled test pack
• Commercially available, FDA cleared preassembled test pack
•ST41 describes two types of PCDs
• Routine BI test pack
• Challenge BI test pack
Ethylene Oxide Sterilization Recommended Monitoring Practices
ANSI/AAMI ST41:2008, Section 10
Routine Load Release/Sterilizer Efficacy Monitoring
• Physical monitoring of cycle• External and internal monitoring of packages• Monitoring of every load with a PCD (routine test pack) containing a BI and a CI or equivalent, commercially available BI PCD
• Ideally, quarantine implants until BI results are known
Ethylene Oxide
BI placed in full load in center
Frequency, in each load Visual, color 48 hour
readout Rapid readout BI for ETO
provides 4hr (not shown)
Hydrogen Peroxide Gas Plasma
Provides evidence that proper sterilization conditions were achieved in 24 hours
Built-in chemical indicator confirms it has been exposed to HP if color changed from red to yellow
Placed in peel pack on bottom rack with tyvek side up 1x per day
CI placed in every load
Monitoring of Sterilizers
Internal Chemical IndicatorValidates the sterilant penetrated the pack or trayAdvantage of the pack control monitor is that it is
inside each pack in multiple locationsDetect local problem
RecommendationsMonitoring of Sterilizers
Following a single positive biological indicator used with a method other than steam, treat as non-sterile all items that have been processed in that sterilizer, dating back to last negative biological indicator. These non-sterile items should be retrieved, if possible, and reprocessed.
Routine Load Release/Routine Sterilizer Efficacy Monitoring
Acceptance criteria• Appropriate readings from physical monitors
• Appropriate readings from CIs
• Negative result from BI in PCD
• Positive BI control result
• Run a control BI, with matching lot #, each day
• Document all results in sterilization cycle record
ANSI/AAMI ST41:2008, Section 10
RecommendationsStorage of Sterile Items
Sterile storage area should be well-ventilated area that provides protection against dust, moisture, and temperature and humidity extremes.
Sterile items should be stored so that packaging is not compromised
Sterilized items should be labeled with a load number that indicates the sterilizer used, the cycle or load number, the date of sterilization, and the expiration date (if applicable)
Conclusions All sterilization processes effective in killing spores Cleaning removes salts and proteins and must precede
sterilization Delivery of sterile products for use in patient care
depends not only on the effectiveness of the sterilization process but also on cleaning, disassembling and packaging of the device, loading the sterilizer, and monitoring
Low-Temperature Sterilization Provide overview of low-temperature sterilization
Characteristics Benefits Monitoring
References Rutala WA, Weber DJ. Disinfection and sterilization: What clinicians need
to know. Clin Infect Dis 2004;39:702 Rutala WA, Weber DJ, HICPAC. CDC guideline for disinfection and
sterilization in healthcare facilities. November 2008. www.cdc.gov Alfa MJ, Olson N, DeGagne P, Hizon R. New low temperature sterilization
technologies: Microbicidal activity and clinical efficiency. In Rutala WA, ed. Disinfection, Sterilization, and Antisepsis in Healthcare. Champlain, NY: Polyscience Publications. 1998:67-78.
Rutala WA, Weber DJ. Clinical effectiveness of low-temperature sterilization technologies. Infect Control Hosp Epidemiol 1998;19:798-804.
Rutala WA, Weber DJ. Disinfection and sterilization. 2013;41:S2